XTVR RX gain cahnges with preamp (6500)

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  • Question
  • Updated 5 years ago
  • Answered
When using XTVR in my 6500 with a 2 meters converter, I experience the following changes.

-10 dB position Noisefloor Pan -105 dBm Smeter S 5,5 Signal S9+5
0 dB position NoiseFloor Pan -118 dBm Smeter S 3,5 Signal S9+5
+10dB position NoiseFloor Pan -123 dBm Smeter S 2,5 Signal S9+5
+20dB position NoiseFloor Pan -128 dBm Smeter S 1,5 Signal S9+5

The signal always peaks the same level, but Noise changes in Smeter and Noise Floor Line in Panadapter.

But if I use the RX A it does not change anything with pream changes.

Luis EA3OG
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Luis del MOlino

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Posted 5 years ago

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Eric - KE5DTO, Official Rep

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Official Response
Luis, I can't tell whether we are talking about a difference in philosophy or whether the radio isn't behaving as designed. So let me try and describe our philosophy and how I think it should work. Then we can argue over whether the philosophy is sound and whether the software behaves in accordance.

At Flex, we want the S-Meter and the Panadapter to reflect the signals at the antenna as accurately as possible. This means that when we put in a 10dB attenuator or a 20dB preamp, we compensate for this fact since it is in the radio and should not change a signal from the antenna.

As such, a reasonably strong (well above the noise floor) signal peak should remain in the same place on the Panadapter as the Preamp setting is changed. SImilarly, if the signal is within the final filter of a Slice, the S-Meter should remain unchanged.

Clearly this adjustment also affects the noise floor as well. To the degree that the noise floor moves down on the Panadapter when you turn the Preamp up shows whether there is really an advantage to having the Preamp at that setting (i.e. if the noise floor doesn't drop, then you are likely limited by the ambient environmental noise as opposed to some limit inside the radio itself).

To the degree that SmartSDR is not behaving in this way, it would be a bug. Given your description, I went back and verified that SmartSDR behaves in the manner described above for all antenna inputs and I didn't find any problems.

Thanks for the question though and the opportunity to describe how this works. It is very different from radios where you twist a knob and the S-Meter value changes while the signal at the antenna never moved.